Modbus RTU vs Modbus TCP: Which Connection Should You Test?
Published September 27, 2026
A practical comparison of Modbus RTU serial communication and Modbus TCP Ethernet communication for commissioning and troubleshooting.
Modbus RTU and Modbus TCP use the same basic application protocol, but the transport and configuration are different. Choosing the right test setup starts with identifying how the PLC, controller, meter or other device is connected.
Modbus RTU
RTU normally uses a serial interface such as RS-485. Typical troubleshooting points include COM port, baud rate, parity, stop bits, slave address and wiring.
Modbus TCP
TCP uses Ethernet and a network endpoint. Check the device IP address, TCP port, network reachability and unit identifier where required.
A useful test sequence
Start with one known register. Use Read Once, confirm the response, then enable polling. If the response is unexpected, inspect HEX traffic and verify the register type, address, quantity and data format.
M_Logger 2.0 supports both RTU and TCP so the same testing workflow can be applied across common industrial setups.